STRAP 3108595 - Caterpillar

Shifting from the NEUTRAL position to the First Speed Forward position with a Running Engine
Illustration 4 g00670981
Transmission Hydraulic Controls in the FIRST SPEED FORWARD position (1) Number 2 clutch solenoid. (2) Number 3 clutch solenoid. (5) Number 5 clutch solenoid. (7) Flow control orifice. (10) Slug. (11) Torque converter inlet ratio valve. (13) Modulating relief valve. (14) Direction selection spool. (18) Selector spool for first speed and for third speed. (19) Pressure differential valve. (20) Load piston. (AA) Speed clutch oil P1. (BB) Direction clutch oil P2. (CC) Torque converter inlet oil P3. (DD) Torque converter outlet oil. (EE) Lubrication oil. (FF) Return oil. (GG) Pilot oil. (HH) Torque converter clutch oil.When the STIC transmission direction control switch is moved to FORWARD and the speed control switch for the STIC transmission is shifted to first speed, solenoids (1) and (5) are activated and solenoid (2) is deactivated. Solenoid (1) moves a spool. Solenoid (1) also directs oil to the top end of direction spool (14). Spool (14) moves downward and pump oil flows around the spool. The pump oil then flows to the Number 2 clutch.Solenoid (5) moves a spool. Solenoid (5) also directs oil to the bottom of speed selection spool (18). Solenoid (2) is deactivated. Solenoid (2) also directs oil from the top end of speed selection spool (18) to the reservoir. Spool (18) moves upward and pump oil flows around the spool to the Number 5 clutch.When the shift to first speed forward is made, the Number 3 clutch is opened to the reservoir. The pressure in the system decreases. Springs move modulating relief valve (13) upward. Springs also move pressure differential valve (19) upward until the large orifice at the top end of valve (19) is closed to pump oil by the valve body.As the pressure differential valve (19) moves upward, the chamber behind load piston (20) opens to the reservoir. This allows the springs to move the load piston downward. The speed clutch oil starts to fill the Number 5 clutch.When the Number 5 clutch is full of oil, the pressure in the speed clutch circuit starts to increase. The increase is felt in the slug chamber of modulating relief valve (13) and in the chamber at the top of pressure differential valve (19) .The oil to pressure differential valve (19) starts to fill the chamber at the top of the valve spool through the small orifice.When the pressure in the Number 5 clutch is approximately 380 kPa (55 psi) pressure differential valve (19) starts to move down. The movement of the valve spool opens the Number 2 clutch to pump oil. The movement of the valve spool also closes a passage from the chamber behind load piston (20) to the reservoir.When the Number 2 clutch is full of oil, the pressure increases in the direction clutch circuit. The increase is felt in the spring chamber of pressure differential valve (19). The combination of the pressure in the spring chamber and the force of